Apart from the obvious kinds of places you can gather data: using Google searches, StatsCan resources, Wikipedia and so on, there are many tools that will enable you to gather or “scrape” data off the web. Here’s a couple articles that review some options:
Planning your infographic
This article from Fast Company does a great job of walking you through the process
Free services to help you design your own infographics:
This layout cheat sheet from Piktochart is quite good. It has lots of tips and advice to follow:
You can also check out their design series, which includes 8 articles.
And here’s a longer piece about the whole process:
And of course, you want to see more infographics about infographics — here’s 11.